This is pretty cute! Simple language, but it has correct grammar, just like children's stories should! And, it would strike a chord with kids who are just starting school. It also shows how much easier it is to make friends than the cuties might think!

One grammar-ie thing - When Willie's teacher says, "'But do not worry, I am sure you will make some friends...'" I think that you should probably contract "do not" and maybe "I am" - it feels a little forced and awkward as is, and picture books tend to feel a little less formal (formal for a kid, stiff and unnatural for adults).

Also, on the page that says, "It was the same thing after recess. We played more with the cars and took a nap", I think that this should be on a facing page with illustrations showing the teacher teaching them about colors, spelling, etc., another picture (on the same page?) of Willie and Billy playing with the cars, and on the facing page, I think you should put "... and took a nap", and have an illustration of them sleeping side by side, looking happily like the best of friends. When I read it, that image very clearly came to mind, but your formatting didn't seem to indicate that, so I thought I'd just let you know that your words called that to mind.

Btw, it's awesome that you can call the images to my head just with these words! I hadn't ever noticed just how evocative you need your language to be to write a good children's book, but you're spot on! Good job!

One tiny little thing - maybe a better intro than "this is my story"? Maybe... "I'm about to start school for the first time" or something? "This is my story" is a little too broad... it's overly simple and has too complex a meaning for a kid to use at the same time... and it also seems to imply some sort of adult experience in Willie. It's just a bit out of place, I thought.

I want to read the next one! If I can remember it, I'll check out your next ones - this is cute! Can I volunteer to send you some illustrations if I get a chance to draw them up?